JPH1137900A - Combustion state detector for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To judge normal combustion state/misfiring state or an abnormal state of wire harness, or the like, correctly for every cylinder of an internal combustion engine, and to specify a failed cylinder and a failed part at the time of inspection, repair or maintenance. SOLUTION: After an ignition coil 10 is driven based on an ignition command signal IGt from an ECU(electronic control unit for internal combustion engine), an ion current flowing between an ignition plug 12 and the ground is detected by means of an ion current detecting resistor 17, an operational amplifier 20, and the like, and converted through a comparator 30 into a signal which is fed through an offset means, i.e., resistors 31, 32, to produce a signal within a specified range corresponding to the ECU 40. Since the ion current signal is not fixed to the power supply voltage or the ground potential when an internal combustion engine is in normal combustion state or misfiring state, normality/abnormality of circuit can be distinguished surely and thereby a failed cylinder and a failed part can be specified easily at the time of inspection, repair or maintenance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion state detecting device for an internal combustion engine that detects a combustion state based on a current flowing between a spark plug disposed in a combustion chamber of the internal combustion engine and a ground.

[0002]

2. Description of the Related Art Conventionally, as a prior art document relating to a combustion state detecting device of an internal combustion engine, there is Japanese Patent Application Laid-Open No. 7-286552.
The one disclosed in Japanese Patent Application Publication No. HEI 10-203 (1995) is known. In this technique, a technique for determining misfire based on an integrated value of an ion current generated by combustion of an internal combustion engine or a determination result of the presence or absence of an ion current by a comparator is disclosed.

[0003]

By the way, in both the case of using the integrated value and the case of using the comparator, the output circuit failure of the combustion state detecting circuit, the disconnection of the wire harness, and the like.
Failure to distinguish between a case where the output for misfire determination is fixed to the power supply voltage or the ground (GND) potential due to a ground short circuit of the wire harness and a case where the ion current output is functioning normally. was there.

More specifically, in a combustion state detection circuit 50 using a comparator 51 as shown in FIG. 3, a combustion state detection circuit 50 is based on a current flowing between a spark plug (not shown) provided in a combustion chamber of an internal combustion engine and a ground. An ion current signal is input to an open collector type comparator 51. Here, when the ion current signal exceeds a predetermined level and the internal combustion engine is in a normal combustion state, the output signal from the comparator 51 is open (off), and when the ion current signal is lower than the predetermined level,
When the internal combustion engine is in a misfire state, the output signal from the comparator 51 is set to L (0 [V]: ON).

As a receiving side of the output signal from the comparator 51 of the combustion state detecting circuit 50, for example, as shown in FIG. 3, the connection terminal 60a side of the fuel injection control circuit 60 is pulled up to a constant voltage of 5 [V]. The pull-up processing is performed via the resistor 61. The voltage at the connection terminal 60a of the fuel injection control circuit 60 is input to the non-inverting (+) terminal of the comparator 62, and the comparison voltage Vref input to the inverting (-) terminal for the combustion state determination is used as the reference voltage. Be compared. The output terminal side of the comparator 62 has a constant voltage of 5
[V].

Here, if the wire harness 55 connecting between the connection terminal 50a of the combustion state detection circuit 50 and the connection terminal 60a of the fuel injection control circuit 60 is disconnected, as shown in FIG. The signal level at that time is the same as the signal level when the internal combustion engine is in a normal combustion state.
[V], even if the wire harness 55 is broken and is in an abnormal state, it cannot be distinguished from a normal combustion state and is erroneously determined. Further, when a ground short circuit occurs in the wire harness 55, as shown in FIG. 4, the signal level at that time and the signal level when the internal combustion engine is in a misfire state are the same 0 [V]. Even if the wire harness 55 is in an abnormal state due to a short circuit, it cannot be distinguished from a misfire state and is erroneously determined.

Further, in the same configuration as FIG. 3, when the internal combustion engine is in a normal combustion state, the output signal from the comparator 51 of the combustion state detection circuit 50 is L (0 [V]: ON). If the output signal from the comparator 51 is open (off) in the misfire state, the wiring harness 55
In this case, it is impossible to distinguish between the case where the wire breakage occurs and the case where the fire is misfired, or the case where the ground short circuit occurs in the wire harness 55 and the case where the wire harness 55 is in the normal combustion state.

Therefore, for example, even if the internal combustion engine is indicated by a warning lamp or the like as being in a misfire state, it is not possible to specify whether the internal combustion engine is in a misfire state or a disconnection / short circuit has occurred in the wire harness 55. , Inspection, repair,
It was difficult to find abnormal spots during maintenance.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and is based on a current flowing between a spark plug disposed in a combustion chamber and a ground for each cylinder of an internal combustion engine. An object of the present invention is to provide a combustion state detection device for an internal combustion engine that can accurately determine a misfiring state or an abnormal state such as a wire harness and easily identify a failed cylinder and a failed part during inspection, repair, and maintenance.

[0010]

According to the first aspect of the present invention, the current flowing between the spark plug and the ground is detected by the combustion state detecting means, and the detected current is detected by the signal converting means. A voltage signal corresponding to the combustion state is output based on the current. Further, the voltage signal output from the signal conversion means is offset to a predetermined range by the offset means. Accordingly, the signal output from the offset means is not fixed to the power supply voltage or the ground potential even when the internal combustion engine is in the normal combustion state or the misfire state, so that the normal / abnormality on the circuit can be ensured. And it is possible to easily specify a failed cylinder and a failed part during inspection, repair, and maintenance.

In the combustion state detecting device for an internal combustion engine, a voltage signal is output from the offset means to the electronic control unit, and the electronic control unit processes the failure determination signal and the combustion state determination signal independently. At the same time, the processing is performed for each cylinder of the internal combustion engine. As a result, a failure can be determined regardless of the combustion state of the internal combustion engine. In addition, it is possible to specify a failed cylinder and a failed part at the time of inspection, repair, and maintenance.

According to a third aspect of the present invention, when the failure determination signal is within a predetermined range in the electronic control unit, the combustion state based on the combustion state determination signal, for example,
The presence / absence of a misfire is determined. When the failure determination signal is out of the predetermined range, the presence / absence of a failure is determined based on the failure determination signal.
Thereby, it is possible to prevent erroneous determination in the combustion state when a failure occurs.

In the combustion state detecting device for an internal combustion engine according to the present invention, it is determined that a failure has occurred when the failure determination signal is continuously out of the predetermined range for a predetermined time in the electronic control unit. This can prevent erroneous determination when noise or the like is superimposed on the signal output from the offset means.

In the combustion state detecting device for an internal combustion engine according to the present invention, when a failure determination signal is larger than a predetermined range in the electronic control unit, a disconnection occurs in a wire harness for electrically connecting the electronic control unit and the offset means. It is determined that there is. As a result, it is possible to specify a failed part at the time of inspection, repair, and maintenance.

According to a sixth aspect of the present invention, when the electronic control unit determines that the failure determination signal is smaller than a predetermined range, the wire harness for electrically connecting the electronic control unit and the offset means is short-circuited to ground. It is determined that there is. As a result, it is possible to specify a failed part at the time of inspection, repair, and maintenance.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below based on examples.

FIG. 1 is a block diagram showing a combustion state detecting device for an internal combustion engine according to an embodiment of the present invention.
Since the internal combustion engine of this embodiment is composed of a plurality of cylinders and has the same configuration of the ignition coil / igniter of each cylinder, the ignition coil / igniter 1 for one cylinder will be described below.

In FIG. 1, reference numeral 10 denotes an ignition coil;
10a is a primary winding of the ignition coil 10, and 10b is a secondary winding of the ignition coil 10. Reference numeral 12 denotes a spark plug provided in a combustion chamber of an internal combustion engine (not shown). Ignition coil 10
The switching element 11 is connected to the primary winding 10a, and for example,
An electronic control unit (hereinafter referred to simply as “EC”) for an internal combustion engine which constitutes a fuel injection control circuit, which will be described later.
U ”) from the connection terminal 1a, and the switching element 11 is turned on, so that the primary winding 10a of the ignition coil 10 is connected to a battery power supply (not shown). The primary current I1 from the + B terminal (connection terminal) is supplied.

A current path in which the secondary current I2 circulates on the secondary winding 10b side of the ignition coil 10 is formed by the ignition plug 12, the secondary winding 10b of the ignition coil 10, the Zener diode 13 and the Zener diode 14. Have been. Here, the Zener diode 14 has a secondary current I2
It is connected in the forward direction with respect to the direction in which the (secondary circulating current) flows. The zener diode 13 is a diode for charging the capacitor 15 serving as an ion current detection power supply connected in parallel with the zener diode 13. Further, a resistor 16 is connected in parallel with the Zener diode 14.

At the time of detecting the ion current, the ion current IION flows from the capacitor 15 to the secondary winding 10b of the ignition coil 10 and the ignition plug 12 in order, and furthermore, the ion current detection resistor 17 from the inverting (-) terminal side of the operational amplifier 20. An ion current IION flows through the ion current detection resistor 17
As a result, an ion current IION is detected. The resistor 21 connected between the inverting (-) terminal and the output terminal of the operational amplifier 20 is an amplifying resistor for setting the gain of the operational amplifier 20.

A voltage signal from the operational amplifier 20 based on the ion current IION is input to an inverting (-) terminal of a comparator 30 built in the ignition coil / igniter 1. The comparator 30 outputs a voltage signal according to the combustion state based on the ion current IION. The output terminal of the comparator 30 is connected to the connection terminal 1b of the ignition coil / igniter 1 via a resistor 31 (resistance value R1). The connection between the resistor 31 and the connection terminal 1b is connected to ground (GND) via a resistor 32 (resistance value R2).
An offset is provided to the voltage signal output from the comparator 30 by these resistors 31 and 32, and the voltage signal is offset to a voltage signal between a comparison voltage VTH1 and a comparison voltage VTH2 in a predetermined range described later. The non-inverting (+) terminal of the comparator 30 receives a predetermined comparison voltage from the resistors 33 and 34.

Connection terminal 1b of ignition coil / igniter 1
Is connected to a connection terminal 40a of the ECU 40 via a wire harness 35, and the connection terminal 1b is connected to a constant power supply 5 [V] via a pull-up resistor 41 (resistance value R3). Therefore, the connection terminal 40a of the ECU 40
, A predetermined voltage divided corresponding to the ON / OFF state of the comparator 30 appears as described later. The voltage at the connection terminal 40a of the ECU 40 is input to the non-inverting (+) terminal of the comparator 42 in the ECU 40, and the comparison voltage Vre input to the inverting (-) terminal for determining the normal combustion state / misfire state.
is compared to f.

The voltage at the connection terminal 40a of the ECU 40 is input to the inverting (-) terminal of the comparator 44 in the ECU 40, and is compared to the non-inverting (+) terminal as the upper limit voltage for abnormality determination. In addition to the comparison with the voltage VTH1, the voltage is inputted to the non-inverting (+) terminal of the comparator 45, and is compared with the comparison voltage VTH2 as the lower limit voltage for abnormality judgment inputted to the inverting (-) terminal. At this time, a potential difference between the comparison voltage VTH1 and the power supply voltage 5 [V] or a potential difference between the comparison voltage VTH2 and the ground (GND) potential is set in consideration of a voltage tolerance on a circuit in the ECU 40 or the like. This prevents erroneous detection based on the power supply voltage or the ground (GND) potential and erroneous detection due to noise. Based on the output signals of the comparators 44 and 45, the microcomputer 48 determines a failure such as disconnection or short circuit.

The output terminal of the comparator 42 is connected to a constant power supply 5 [V] via a resistor 43, and the output terminals of the comparators 44 and 45 are connected to a constant power supply 5 [V] via a resistor 44. ing. Output signals (voltages) from the output terminals of the comparators 42, 44, and 45 are input to the microcomputer 48. In the microcomputer 48, the comparator 42
Is determined on the basis of the output signal.

The microcomputer 48 has a CP as a central processing unit for executing various known arithmetic processing.
U, a ROM storing a control program, a RAM storing various data, a B / U (backup) RAM, an input / output circuit, and a logical operation circuit including a bus line connecting them.

FIG. 2 shows a comparison between the normal combustion state, the misfire state, the disconnection of the wire harness 35, and the ground short-circuit of the wire harness 35 in the combustion state detection device for an internal combustion engine according to one embodiment of the present invention. Vessels 42, 44,
It is explanatory drawing which shows the signal level from 45.

First, in the ignition coil / igniter 1, when the ion current signal based on the current flowing between the ignition plug 12 and the ground exceeds a predetermined level and the internal combustion engine is in a normal combustion state, the output signal from the comparator 30 is output. Is open (off). Then, the resistor 31 does not operate, and the signal level at the connection terminal 40a of the ECU 40 is divided by the resistance value R2 of the resistor 32 and the resistance value R3 of the resistor 41 from the constant power supply 5 [V]. ) Voltage v1 [V]
Becomes

[0028]

V1 = 5 × {R2 / (R2 + R3)} (1) As shown in FIG. 2, this voltage v1 is larger than the comparison voltage Vref of the comparator 42 and the comparison voltage of the comparator 44. The signal level is lower than VTH1. Therefore, the comparator 42,
The output terminal voltages of 44 and 45 are both 5 [V]. That is, since the voltage signal input via the connection terminal 40a is within the predetermined range between the comparison voltage VTH1 and the comparison voltage VTH2, the microcomputer 48 determines whether or not there is a misfire based on the output signal of the comparator 42, It is determined that combustion has occurred.

Next, in the ignition coil / igniter 1, when the ion current signal based on the current flowing between the ignition plug 12 and the ground is below a predetermined level and the internal combustion engine is in a misfire state, the output signal from the comparator 30 is output. Is L (0
[V]: ON). Then, the resistor 31 operates, and E
The signal level of the connection terminal 40a of the CU 40 is
[V] is the resistance R2 of the resistor 32 and the resistance R1 of the resistor 31
And the resistance R3 of the resistor 41 and the parallel resistance of the resistor R3.
When the resistance value R1≪the resistance value R2, it can be approximated to a voltage v2 [V] represented by the following equation (2).

[0030]

[Expression 2] v2 ≒ 5 × [(R1 // R2) / ｛(R1 // R2) + R3 ＋] (2) where (R1 // R2) = (R1 × R2) / (R1 + R
2)

As shown in FIG. 2, the voltage v2 is a signal level lower than the comparison voltage Vref of the comparator 42 and higher than the comparison voltage VTH2 of the comparator 45. Therefore,
The output terminal voltage of the comparator 42 becomes 0 [V],
The output terminal voltage of 4, 45 becomes 5 [V]. At this time,
As in the case of normal combustion, the microcomputer 48 determines that a misfire has occurred based on the output of the comparator 42.

Next, when the wire harness 35 connecting between the connection terminal 1b of the ignition coil / igniter 1 and the connection terminal 40a of the ECU 40 is disconnected, the resistance 3
Neither 1 nor 32 acts, and the signal level of the connection terminal 40a of the ECU 40 becomes the voltage of the constant power supply 5 [V] as it is. This voltage is, as shown in FIG.
The signal level is higher than the comparison voltage Vref of No. 2 and higher than the comparison voltage VTH1 of the comparator 44. Therefore, the output terminal voltage of the comparator 42 becomes 5 [V], and the output terminal voltage of the comparator 44 becomes 0 [V].

That is, since the voltage signal input from the connection terminal 40a is out of the predetermined range including the comparison voltage VTH1 and the comparison voltage VTH2 (greater than the comparison voltage VTH1),
The microcomputer 48 performs a failure determination based on this signal. In this embodiment, when the voltage signal continuously input from the connection terminal 40a for a predetermined time is larger than a predetermined range, it is determined that the wire harness 35 is disconnected.

Further, when a ground short circuit occurs in the wire harness 35 connecting the connection terminal 1b of the ignition coil / igniter 1 and the connection terminal 40a of the ECU 40,
The resistors 31 and 32 do not work together, and the ECU 40
Is connected to the ground, and its signal level becomes 0 [V]. This voltage is a signal level lower than the comparison voltage Vref of the comparator 42 and lower than the comparison voltage VTH2 of the comparator 45, as shown in FIG. Therefore, both output terminal voltages of the comparators 42 and 44 become 0 [V]. At this time, similarly to the case of the disconnection, the microcomputer 48 performs the failure determination based on the output of the comparator 45. In this embodiment, when the voltage signal input from the connection terminal 40a continuously for a predetermined time is smaller than the predetermined range, it is determined that the wire harness 35 is short-circuited.

As described above, the combustion state detecting device of the internal combustion engine according to the present embodiment detects the current flowing between the ignition plug 12 provided in the combustion chamber and the ground for each cylinder of the internal combustion engine, and Spark plug 12 for detecting the combustion state of the engine, capacitor 15, ion current detection resistor 17, operational amplifier 2
A signal converting means including a combustion state detecting means comprising a resistor 0, a resistor 21 and the like; a comparator 30 outputting a voltage signal corresponding to a combustion state based on the current detected by the combustion state detecting means; And offset means consisting of resistors 31 and 32 for offsetting the voltage signal output from the inverter to a predetermined range (comparison voltages VTH1 to VTH2).

Therefore, the ignition plug 12 as a combustion state detecting means, the capacitor 15, the ion current detecting resistor 1
7, the ignition flag 12 by the operational amplifier 20, the resistor 21, etc.
A current flowing between the power supply and the ground is detected, and a voltage signal corresponding to the combustion state is output based on the detected current by the comparator 30 or the like as a signal converting means. Further, the voltage signal output from the comparator 30 or the like as signal conversion means via the resistors 31 and 32 as offset means is offset to a predetermined range. Thus, even when the internal combustion engine is in a normal combustion state or a misfire state, the signal output via the resistors 31 and 32 is not fixed to the power supply voltage or the ground potential, and the normal circuit / Abnormalities can be reliably determined, and it becomes easy to specify a failed cylinder and a failed part during inspection, repair, and maintenance.

Further, the combustion state detecting device for an internal combustion engine according to the present embodiment includes an ECU 40 for receiving a signal output from offset means including resistors 31 and 32.
Monitor the voltage signal output from the offset means, and determine a failure determination signal for determining a failure of the signal conversion means including the wire harness 35 and the comparator 30 for transmitting the signal, and determine a combustion state of the internal combustion engine. And independently for each cylinder of the internal combustion engine. As a result, a voltage signal is output to the ECU 40 via the resistors 31 and 32 as offset means, and the ECU 40 independently processes the failure determination signal and the combustion state determination signal, and processes the failure determination signal and the combustion state determination signal for each cylinder of the internal combustion engine. Is done. As a result, a failure can be determined regardless of the combustion state of the internal combustion engine. In addition, inspection, repair,
It is easy to specify a failed cylinder and a failed part during maintenance.

The ECU 40 determines the combustion state of the internal combustion engine based on the combustion state determination signal when the failure determination signal is within a predetermined range (comparison voltages VTH1 to VTH2). When the failure determination signal is out of the predetermined range (comparison voltages VTH1 to VTH2), the presence or absence of a failure is determined based on the failure determination signal. That is, when the failure determination signal is within a predetermined range, the ECU 40 determines the combustion state, for example, the presence or absence of a misfire based on the combustion state determination signal. When the failure determination signal is outside the predetermined range, the ECU 40 determines the failure based on the failure determination signal. The presence or absence is determined. As a result, erroneous determination in the combustion state when a failure occurs can be prevented.

Further, in the combustion state detecting device for an internal combustion engine according to the present embodiment, the ECU 40 determines that a failure has occurred when the failure determination signal is continuously out of a predetermined range (comparison voltage VTH1 to VTH2) for a predetermined time. Is what you do. That is, ECU
At 40, it is determined that a failure has occurred when the failure determination signal is out of the predetermined range for a predetermined time. This can prevent erroneous determination when noise or the like is superimposed on a signal output via the resistors 31 and 32 as offset means.

Further, in the combustion state detecting device for an internal combustion engine according to the present embodiment, when the failure determination signal is larger than a predetermined range (comparison voltage VTH1 to VTH2) in the ECU 40, the ECU 40 and the offset means including the resistors 31 and 32 are electrically connected. It is determined that a disconnection has occurred in the wire harness 35 to be electrically connected. That is, when the failure determination signal is higher than the comparison voltage VTH1 in the ECU 40, it is determined that the wire harness 35 that electrically connects the ECU 40 and the resistors 31 and 32 as the offset means is disconnected. As a result, a failure site at the time of inspection, repair, or maintenance can be specified.

In addition, in the internal combustion engine combustion state detecting device of this embodiment, when the ECU 40 determines that the failure determination signal is smaller than a predetermined range (comparison voltages VTH1 to VTH2), the ECU 40 and the offset means including the resistors 31 and 32 are electrically connected. It is determined that the wire harness 35 to be electrically connected is short-circuited to the ground. That is, when the failure determination signal is smaller than the comparison voltage VTH2, the ECU 40 determines that the wire harness 35 that electrically connects the ECU 40 and the resistors 31 and 32 as offset means is short-circuited to the ground. As a result, a failure site at the time of inspection, repair, or maintenance can be specified.

Although the processing of the microcomputer 48 is not described in detail in the above embodiment, the comparator 4
When the signal levels from the signals 2, 44 and 45 are not within the normal range for a predetermined period of time, it is determined to be abnormal, and as a subsequent process, a determination signal for input system failure diagnosis is output for each cylinder of the internal combustion engine. Things.

In the above embodiment, the comparator 42,
Signal levels from the output terminals 44 and 45 are input to the microcomputer 48 and used, for example, for stopping fuel supply to a failed cylinder in fuel injection control. However, the present invention is not limited to this. Instead, a warning lamp or the like can be lit directly using a hardware configuration at a signal level from the output terminals of the comparators 42, 44, and 45.

In the above embodiment, the resistors 31 and 32 as offset means are connected to the ignition coil / igniter 1.
However, the present invention is not limited to this, and may be provided on the ECU 40 side, or only one of the resistors may be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a combustion state detection device for an internal combustion engine according to an example of an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing signal levels in a normal / abnormal judgment of a combustion state detection device for an internal combustion engine according to one example of an embodiment of the present invention.

FIG. 3 is a configuration diagram showing a conventional combustion state detecting device for an internal combustion engine.

FIG. 4 is an explanatory diagram showing signal levels in a normal / abnormal judgment of a conventional combustion state detecting device for an internal combustion engine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ignition coil / igniter 10 Ignition coil 11 Switching element 12 Spark plug 20 Operational amplifier 35 Wire harness 40 ECU (Electronic control unit for internal combustion engine)

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[Procedure amendment]

[Submission date] January 30, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0036

[Correction method] Change

[Correction contents]

Therefore, the ignition plug 12 as a combustion state detecting means, the capacitor 15, the ion current detecting resistor 1
7, the operational amplifier 20, ignited by a resistor 21, etc. Plug 12
A current flowing between the power supply and the ground is detected, and a voltage signal corresponding to the combustion state is output based on the detected current by the comparator 30 or the like as a signal converting means. Further, the voltage signal output from the comparator 30 or the like as signal conversion means via the resistors 31 and 32 as offset means is offset to a predetermined range. Thus, even when the internal combustion engine is in a normal combustion state or a misfire state, the signal output via the resistors 31 and 32 is not fixed to the power supply voltage or the ground potential, and the normal circuit / Abnormalities can be reliably determined, and it becomes easy to specify a failed cylinder and a failed part during inspection, repair, and maintenance.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Tomoyuki Nomura 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation

Claims (6)

[Claims] An electric current flowing between a spark plug disposed in a combustion chamber and a ground for each cylinder of an internal combustion engine is detected.
Combustion state detection means for detecting a combustion state of the internal combustion engine; signal conversion means for outputting a voltage signal corresponding to a combustion state based on the current detected by the combustion state detection means; and output from the signal conversion means. And an offset unit for offsetting the voltage signal to a predetermined range. 2. An electronic control unit for receiving a signal output from the offset means, wherein the electronic control unit monitors a voltage signal output from the offset means, and transmits the signal to the wiring harness or the signal. A failure determination signal for determining a failure of the conversion means and a combustion state determination signal for determining a combustion state of the internal combustion engine are independently processed, and are processed for each cylinder of the internal combustion engine. The combustion state detecting device for an internal combustion engine according to claim 1, wherein: 3. The electronic control unit determines a combustion state of the internal combustion engine based on the combustion state determination signal when the failure determination signal is within the predetermined range, and the failure determination signal is out of the predetermined range. 3. The method according to claim 2, wherein the presence or absence of a failure is determined based on the failure determination signal.
A combustion state detection device for an internal combustion engine according to claim 1. 4. The electronic control unit according to claim 2, wherein the electronic control unit determines that a failure has occurred when the failure determination signal is outside the predetermined range for a predetermined time. A combustion state detection device for an internal combustion engine according to the above. 5. The electronic control unit according to claim 1, wherein when the failure determination signal is larger than the predetermined range, the electronic control unit determines that a disconnection has occurred in a wire harness that electrically connects the electronic control unit and the offset means. The combustion state detection device for an internal combustion engine according to any one of claims 2 to 4, characterized in that: 6. The electronic control unit determines that a wire harness that electrically connects the electronic control unit and the offset means is short-circuited to ground when the failure determination signal is smaller than the predetermined range. The combustion state detecting device for an internal combustion engine according to any one of claims 2 to 5, characterized in that: